A liquid crystal display apparatus has been utilized in the display segments of personal computers (PC), word processors, liquid crystal televisions, clocks or watches, desktop calculators and others. Recent years have witnessed advances in the construction of infrastructures for telecommunication systems such as internets and in the network consolidation of information through the computer-communications equipment integration. For an efficient utilization of such networks, currently, portable information terminals typified by PDA (Personal Digital Assistance) have been developed, as well as further-downsized mobile personal computers having reduced thickness and weight compared with present notebook-sized personal computers.
Since portability is required of such equipments, it is necessary to reconcile realization for a battery operating a longer time with the need for downsizing and reducing thickness of such equipments. Displays using in such equipment, therefore, demand reduced thickness, reduced weight and low power consumption. A reflective (reflecting type) liquid crystal display apparatus is considered to be the most promising one since the apparatus satisfying these demands.
As a liquid crystal display unit constituting the reflective liquid crystal display apparatus, there is known a variety of elements such as TN (Twisted Nematic) and STN (Super Twisted Nematic) elements, but elements utilizing single polarizing plate type is advantageous to color display and high-definition display.
In such a reflective liquid crystal unit, it is necessary to make the best possible use of a natural light (available light) or an ambient light (external light) for illuminating the display screen by efficiently inducing an incident light on a liquid crystal layer, by scattering a light reflected from an electrode of a liquid crystal cell to an extent not deteriorating visibility and by preventing total reflection.
Concerning a reflective liquid crystal apparatus utilizing single polarizing plate, in Photofabrication Symposium '92 sponsored by the Japanese Society of Printing, the fundamental technology was introduced, as well as the liquid crystal display apparatus having an enlarged viewing angle of the display screen through the prevention of total reflection by using a surface-corrugated metal thin film as the lower electrode. However, in diffusing and reflecting plate system, in order to enhance the directionality of a diffused and reflected light, it is necessary that configuration and distribution of the corrugated (uneven) part of the reflecting plate is accurately controlled, resulting in a high cost. Further, in order to realize high-quality image, it is necessary that the corrugated (uneven) part of the reflection electrode is smoothed with resin-coating etc. for keeping the thickness of the liquid crystal part uniform. However, such a complex technique further makes lowering of production cost and stability in quality harder.
In addition to such a diffusing and reflecting plate system, there has been also known a liquid crystal display apparatus with a transmissive light-diffusing sheet. For example, Japanese Patent Publication No. 8430/1986 (JP-61-8430B) discloses a liquid crystal display apparatus comprising a polarizing layer formed on a front side of a liquid crystal cell, and a light-diffusing layer laminated on the polarizing layer. However, in the transmissive light-diffusing sheet system, since a member such as a substrate is interposed between a light-diffusing sheet and a liquid crystal part, problems such as ghost and blur of images on the display surface are inevitable.
To improve image clearness or definition, Japanese Patent Application Laid-Open No. 323196/1999 (JP-11-323196A) discloses an internal light-diffusing layer system in which a light-diffusing layer is disposed on a surface of a substrate constituting a liquid crystal part or member (liquid crystal cell), and the light-diffusing layer has a resin bead diffused in a transparent resin matrix. However, in the islands-in-an ocean structure of such a fine particle-diffused mode, the diffused light expands according to Gaussian distribution in principle. Thus, it is impossible to efficiently utilize the diffused light for luminance of the display, and display images to uniformly and brightly on the display screen.
Further, since it is necessary to keep the thickness of the liquid crystal cell uniform in order to ensure high-quality image, a scattering layer having a smooth surface must be formed. However, in a method which comprises coating or applying a substrate with a coating liquid composition composed of a transparent resin matrix and a resin bead and drying the substrate to form a layer, it is difficult to obtain a diffusing layer having a smooth surface because a resin bead in the vicinity of the surface generates an uneven structure depending on volume change of the resin involved in the drying step. Further, in a method using a resin bead, it is necessary to control the distribution in the particle size of the resin bead stringently, and as a result, the method has a disadvantage for cost. To form a diffusing layer having a highly smooth surface, a method which comprises coating a liquid mixture of a polymerizable monomer and a resin bead, and polymerizing the mixture with applying an ultraviolet ray is suggested, but the method is deteriorated in productivity.
It is, therefore, an object of the present invention to provide a light-diffusing layer having a smooth surface and capable of effectively obtaining high-quality image, and a process of producing the same.
It is another object of the present invention to provide a light-diffusing layer which ensures uniform and bright display of an image on a screen in an internal light-diffusing layer system having the light-diffusing layer formed on a surface of a substrate constituting a liquid crystal cell, and a process of producing the same.
It is still another object of the present invention to provide a light-diffusing layer useful for efficiently illuminating a display surface with a natural light or an ambient light in a reflective liquid crystal display apparatus, and a process of producing the same.